FunctionImport: Use IRMover directly.

The importer was previously using ModuleLinker in a sort of "IRMover mode". Use
IRMover directly instead in order to remove a level of indirection.

I will remove all importing support from ModuleLinker in a separate
change.

Differential Revision: https://reviews.llvm.org/D29468

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@294014 91177308-0d34-0410-b5e6-96231b3b80d8
4 files changed